The present invention relates to a disturbing agent against intercommunication between different sexes of insects. More particularly, the invention relates to an effective preparation of a sex pheromone compound as a disturbing agent against intercommunication between different sexes of certain lepidopteral insects, such as tomato pinworms (Keiferia lycopersicella) for the purpose of population control.
It is an already established technology in agriculture and horticulture to control the population of pest insects by utilizing the sex pheromone of the particular species of the insects which acts as a disturbing agent against intercommunication between different sexes of the species.
As is known, for example, most of the sex pheromones of various lepidopteral insects, such as tomato pinworms, light-brown apple worms, omnivorous leaf rollers, peach twig borers, spiny bollworms and the like as notorious pests in agriculture are chemically each an aliphatic alcohol having at least one double bond or an acetic acid ester or aldehyde derived from the alcohol. These aliphatically unsaturated compounds each have geometrical isomers including the E-isomer and Z-isomer relative to the steric configuration at the double bond. It is known that the E-isomers only play an important role in the activity of the compound as the sex pheromone of the insects so that it would be desirable that the preparation of a sex pheromone contains the E-isomer in a purity as high as possible in order that an increased activity of disturbing the intercommunication between different sexes of the insects can be obtained.
There is, however, no known industrial method which is generally applicable to the selective preparation of the E-isomers of these sex pheromone compounds. For example, usual methods for the synthesis of these unsaturated organic compounds lead to the formation of substantially the Z-isomer alone so that the desired E-isomer must be prepared by the isomerization treatment of the Z-isomer followed by separation of the isomers, for example, by the urea separation method. Alternatively, the Birch's method of reducing reaction is applicable. Each of these methods is far from industrial applicability due to the very low productivity of the desired E-isomers. This is the reason for the use of sex pheromone preparation which is a mixture of the E- and Z-isomers mainly composed of the E-isomer in admixture with an unavoidable minor amount of the Z-isomer in an object of population control of pest insects for which only the E-isomer is effective according to the generally accepted understanding.
As is mentioned above, it is an extremely difficult matter to industrially prepare an E-isomer of such an unsaturated compound in a sufficiently high purity so that E-isomers of high purity are available only as an extremely expensive chemical reagent. Needless to say, such an extremely expensive chemical reagent cannot be used in the agricultural and horticultural applications as a sex pheromone preparation for population control of pests. Accordingly, conventional sex pheromone preparations under practical applications are usually composed of the E-isomer and the Z-isomer as a mixture in such a proportion that, as a rough measure, the content of the E-isomer is at least 4 times of that of the Z-isomer.